[pstricks] Re: Hyperbolas

[Jacques L'helgoualc'h]

Jacques L'helgoualc'h a écrit, lundi 7 février 2005, à 17:36 :
[...] 
Yet another improvement

\makeatletter
\def\psthyperbola{\pst at object{psthyperbola}}
\def\psthyperbola at i#1#2{%
  \pst at killglue
  \begingroup
  \use at par
  \psthyperbola at ii{#1}{#2}
  \psthyperbola at ii{#1 neg}{#2}% second branch
  \endgroup
}
\def\psthyperbola at ii#1#2{% a b
  \addto at pscode{%
    /a {#1} bind def
    /b {#2} bind def
    /d {2 1 t dup mul sub div} bind def}% d = 2/(1 - t^2)
  \parametricplot{-.99}{.99}{%
    a d 1 sub mul % (1 + t^2)/(1 - t^2) = -1 + 2/(1 - t^2)
    b t d mul mul}
}
\makeatother

but d depends on t: I feel it should be (re)defined inside the
parametricplot loop?
-- 
Jacques L'helgoualc'h